There is a requirement in many industries to monitor the temperature of materials moving along conveyor belts. Conventionally, such monitoring is performed using a single spot or point pyrometer directed towards the belt. Such measurement techniques are of limited value as they only offer crude indications of temperature within the area upon which the spot is focussed. If the spot size is too large then small temperature anomalies, particularly those smaller than the spot size, may be missed. Alarms associated with point pyrometers are limited to an instantaneous local high/low threshold alert in the area of their spot which often lead to false or missed alarms.